Load control system providing power and communication over AC line wiring

ABSTRACT

A load control system comprises a main load control device and a remote load control device, which does not require a neutral connection and allows for feedback at the remote load control device. The main device and the remote load control device are adapted to be coupled between an AC power source and an electrical load. The main load control device comprises a load control circuit for controlling the amount of power delivered to the electrical load. The main load control device is operable to enable a charging path to allow the remote load control device to charge a power supply during a first time period of a half-cycle of the AC power source. The main load control device and the remote load control device are operable to communicate with each other during a second time period of the half-cycle.

RELATED APPLICATIONS

This application is a continuation application of co-pending,commonly-assigned U.S. patent application Ser. No. 13/540,662, filedJul. 3, 2012, which is a continuation application of commonly-assignedU.S. patent application Ser. No. 12/959,939, filed Dec. 3, 2010, nowU.S. Pat. No. 8,242,708, issued Aug. 14, 2012, which is a continuationapplication of commonly-assigned U.S. patent application Ser. No.12/106,614, filed Apr. 21, 2008, now U.S. Pat. No. 7,872,429, issuedJan. 18, 2011, which is a non-provisional application ofcommonly-assigned U.S. Provisional Application Ser. No. 60/925,782,filed Apr. 23, 2007, and U.S. Provisional Application Ser. No.61/016,027, filed Dec. 21, 2007, all entitled MULTIPLE LOCATION LOADCONTROL SYSTEM, the entire disclosures of which are hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to multiple location load control systemshaving multiple smart load control devices, and more particularly, amultiple location dimming system that includes a smart dimmer and one ormore remote dimmers for controlling the amount of power delivered to alighting load, where all of the smart dimmers and the remote dimmers areoperable to display a present intensity level of the lighting load on avisual indicator.

2. Description of the Related Art

Three-way and four-way switch systems for use in controlling electricalloads, such as lighting loads, are known in the art. Typically, theswitches are coupled together in series electrical connection between analternating-current (AC) power source and the lighting load. Theswitches are subjected to an AC source voltage and carry full loadcurrent between the AC power source and the lighting load, as opposed tolow-voltage switch systems that operate at low voltage and low current,and communicate digital commands (usually low-voltage logic levels) to aremote controller that controls the level of AC power delivered to theload in response to the commands. Thus, as used herein, the terms“three-way switch”, “three-way system”, “four-way switch”, and “four-waysystem” mean such switches and systems that are subjected to the ACsource voltage and carry the full load current.

A three-way switch derives its name from the fact that it has threeterminals and is more commonly known as a single-pole double-throw(SPDT) switch, but will be referred to herein as a “three-way switch”.Note that in some countries a three-way switch as described above isknown as a “two-way switch”.

A four-way switch is a double-pole double-throw (DPDT) switch that iswired internally for polarity-reversal applications. A four-way switchis commonly called an intermediate switch, but will be referred toherein as a “four-way switch”.

In a typical, prior art three-way switch system, two three-way switchescontrol a single lighting load, and each switch is fully operable toindependently control the load, irrespective of the status of the otherswitch. In such a three-way switch system, one three-way switch must bewired at the AC power source side of the system (sometimes called “lineside”), and the other three-way switch must be wired at the lightingload side of the system.

FIG. 1A shows a standard three-way switch system 100, which includes twothree-way switches 102, 104. The switches 102, 104 are connected betweenan AC power source 106 and a lighting load 108. The three-way switches102, 104 each include “movable” (or common) contacts, which areelectrically connected to the AC power source 106 and the lighting load108, respectively. The three-way switches 102, 104 also each include twofixed contacts. When the movable contacts are making contact with theupper fixed contacts, the three-way switches 102, 104 are in position Ain FIG. 1A. When the movable contacts are making contact with the lowerfixed contact, the three-way switches 102, 104 are in position B. Whenthe three-way switches 102, 104 are both in position A (or both inposition B), the circuit of system 100 is complete and the lighting load108 is energized. When switch 102 is in position A and switch 104 is inposition B (or vice versa), the circuit is not complete and the lightingload 108 is not energized.

Three-way dimmer switches that replace three-way switches are known inthe art. An example of a three-way dimmer switch system 150, includingone prior art three-way dimmer switch 152 and one three-way switch 104is shown in FIG. 1B. The three-way dimmer switch 152 includes a dimmercircuit 152A and a three-way switch 152B. A typical, AC phase-controldimmer circuit 152A regulates the amount of energy supplied to thelighting load 108 by conducting for some portion of each half-cycle ofthe AC waveform, and not conducting for the remainder of the half-cycle.Because the dimmer circuit 152A is in series with the lighting load 108,the longer the dimmer circuit conducts, the more energy will bedelivered to the lighting load 108. Where the lighting load 108 is alamp, the more energy that is delivered to the lighting load 108, thegreater the light intensity level of the lamp. In a typical dimmingoperation, a user may adjust a control to set the light intensity levelof the lamp to a desired light intensity level. The portion of eachhalf-cycle for which the dimmer conducts is based on the selected lightintensity level. The user is able to dim and toggle the lighting load108 from the three-way dimmer switch 152 and is only able to toggle thelighting load from the three-way switch 104. Since two dimmer circuitscannot be wired in series, the three-way dimmer switch system 150 canonly include one three-way dimmer switch 152, which can be located oneither the line side or the load side of the system.

A four-way switch system is required when there are more than two switchlocations from which to control the load. For example, a four-way systemrequires two three-way switches and one four-way switch, wired in wellknown fashion, so as to render each switch fully operable toindependently control the load irrespective of the status of any otherswitches in the system. In the four-way system, the four-way switch isrequired to be wired between the two three-way switches in order for allswitches to operate independently, i.e., one three-way switch must bewired at the AC source side of the system, the other three-way switchmust be wired at the load side of the system, and the four-way switchmust be electrically situated between the two three-way switches.

FIG. 1C shows a prior art four-way switching system 180. The system 180includes two three-way switches 102, 104 and a four-way switch 185. Thefour-way switch 185 has two states. In the first state, node A1 isconnected to node A2 and node B1 is connected to node B2. When thefour-way switch 185 is toggled, the switch changes to the second statein which the paths are now crossed (i.e., node A1 is connected to nodeB2 and node B1 is connected to node A2). Note that a four-way switch canfunction as a three-way switch if one terminal is simply not connected.

FIG. 1D shows another prior art switching system 190 containing aplurality of four-way switches 185. As shown, any number of four-wayswitches can be included between the three-way switches 102, 104 toenable multiple location control of the lighting load 108.

Multiple location dimming systems employing a smart dimmer and one ormore specially-designed remote (or “accessory”) dimmers have beendeveloped. The remote dimmers permit the intensity level of the lightingload to be adjusted from multiple locations. A smart dimmer is one thatincludes a microcontroller or other processing means for providing anadvanced set of control features and feedback options to the end user.For example, the advanced features of a smart dimmer may include aprotected or locked lighting preset, fading, and double-tap to fullintensity. The microcontroller controls the operation of thesemiconductor switch to thus control the intensity of the lighting load.

To power the microcontroller, the smart dimmers include power supplies,which draw a small amount of current through the lighting load when thesemiconductor switch is non-conductive each half-cycle. The power supplytypically uses this small amount of current to charge a storagecapacitor and develop a direct-current (DC) voltage to power themicrocontroller. An example of a multiple location lighting controlsystem, including a wall-mountable smart dimmer switch andwall-mountable remote switches for wiring at all locations of a multiplelocation dimming system, is disclosed in commonly assigned U.S. Pat. No.5,248,919, issued on Sep. 28, 1993, entitled LIGHTING CONTROL DEVICE,which is herein incorporated by reference in its entirety.

Referring again to the system 150 of FIG. 1B, since no load currentflows through the dimmer circuit 152A of the three-way dimmer switch 152when the circuit between the AC power source 106 and the lighting load108 is broken by either three-way switch 152B or 104, the dimmer switch152 is not able to include a power supply and a microcontroller. Thus,the dimmer switch 152 is not able to provide the advanced set offeatures of a smart dimmer to the end user.

FIG. 2 shows an example multiple location lighting control system 200including one wall-mountable smart dimmer 202 and one wall-mountableremote dimmer 204. The dimmer 202 has a hot (H) terminal for receipt ofan AC source voltage provided by an AC power source 206, and adimmed-hot (DH) terminal for providing a dimmed-hot (orphase-controlled) voltage to a lighting load 208. The remote dimmer 204is connected in series with the DH terminal of the dimmer 202 and thelighting load 208, and passes the dimmed-hot voltage through to thelighting load 208.

The dimmer 202 and the remote dimmer 204 both have actuators to allowfor raising, lowering, and toggling on/off the light intensity level ofthe lighting load 208. The dimmer 202 is responsive to actuation of anyof these actuators to alter the intensity level or to power the lightingload 208 on/off accordingly. In particular, an actuation of an actuatorat the remote dimmer 204 causes an AC control signal, or partiallyrectified AC control signal, to be communicated from that remote dimmer204 to the dimmer 202 over the wiring between the accessory dimmer (AD)terminal of the remote dimmer 204 and the AD terminal of the dimmer 202.The dimmer 202 is responsive to receipt of the control signal to alterthe dimming level or toggle the load 208 on/off. Thus, the load can befully controlled from the remote dimmer 204.

The user interface of the dimmer 202 of the multiple location lightingcontrol system 200 is shown in FIG. 3. As shown, the dimmer 202 mayinclude a faceplate 310, a bezel 312, an intensity selection actuator314 for selecting a desired level of light intensity of a lighting load208 controlled by the dimmer 202, and a control switch actuator 316. Anactuation of the upper portion 314A of the actuator 314 increases orraises the light intensity of the lighting load 208, while an actuationof the lower portion 314B of the actuator 314 decreases or lowers thelight intensity.

The dimmer 202 may also include a visual display in the form of aplurality of light sources 318, such as light-emitting diodes (LEDs).The light sources 318 may be arranged in an array (such as a lineararray as shown), and are illuminated to represent a range of lightintensity levels of the lighting load 208 being controlled. Theintensity levels of the lighting load 208 may range from a minimumintensity level, which may be the lowest visible intensity, but whichmay be “full off”, or 0%, to a maximum intensity level, which istypically “full on”, or substantially 100%. Light intensity level istypically expressed as a percent of full intensity. Thus, when thelighting load 208 is on, light intensity level may range from 1% tosubstantially 100%.

FIG. 4 is a simplified block diagram of the dimmer 202 and the remotedimmer 204 of the multiple location lighting control system 200. Thedimmer 202 includes a bidirectional semiconductor switch 420, e.g., atriac or two field-effect transistors (FETs) in anti-series connection,coupled between the hot terminal H and the dimmed-hot terminal DH, tocontrol the current through, and thus the light intensity of, thelighting load 208. The semiconductor switch 420 has a control input (orgate), which is connected to a gate drive circuit 424. The input to thegate renders the semiconductor switch 420 conductive or non-conductive,which in turn controls the power supplied to the lighting load 208. Thegate drive circuit 424 provides control inputs to the semiconductorswitch 420 in response to command signals from a microcontroller 426.

The microcontroller 426 receives inputs from a zero-crossing detector430 and a signal detector 432 and controls the semiconductor switch 420accordingly. The microcontroller 426 also generates command signals to aplurality of LEDs 418 for providing feedback to the user of the dimmer202. A power supply 428 generates a DC output voltage V_(CC) to powerthe microcontroller 426. The power supply is coupled between the hotterminal H and the dimmed hot terminal DH.

The zero-crossing detector 430 determines the zero-crossings of theinput AC supply voltage from the AC power supply 206. A zero-crossing isdefined as the time at which the AC supply voltage transitions frompositive to negative polarity (i.e., a negative-going zero-crossing), orfrom negative to positive polarity (i.e., a positive-goingzero-crossing), at the beginning of each half-cycle. The zero-crossinginformation is provided as an input to microcontroller 426. Themicrocontroller 426 provides the gate control signals to operate thesemiconductor switch 420 to provide voltage from the AC power source 206to the lighting load 208 at predetermined times relative to thezero-crossing points of the AC waveform.

Generally, two techniques are used for controlling the power supplied tothe lighting load 208: forward phase control dimming and reverse phasecontrol dimming. In forward phase control dimming, the semiconductorswitch 420 is turned on at some point within each AC line voltagehalf-cycle and remains on until the next voltage zero-crossing. Forwardphase control dimming is often used to control energy to a resistive orinductive load, which may include, for example, a magnetic low-voltagetransformer or an incandescent lamp. In reverse phase control dimming,the semiconductor switch 420 is turned on at the zero-crossing of the ACline voltage and turned off at some point within each half-cycle of theAC line voltage. Reverse phase control is often used to control energyto a capacitive load, which may include, for example, an electroniclow-voltage transformer. Since the semiconductor switch 420 must beconductive at the beginning of the half-cycle, and be able to be turnedoff with in the half-cycle, reverse phase control dimming requires thatthe dimmer have two FETs in anti-serial connection, or the like.

The signal detector 432 has an input 440 for receiving switch closuresignals from momentary switches T, R, and L. Switch T corresponds to atoggle switch controlled by the switch actuator 316, and switches R andL correspond to the raise and lower switches controlled by the upperportion 314A and the lower portion 314B, respectively, of the intensityselection actuator 314.

Closure of switch T connects the input of the signal detector 432 to theDH terminal of the dimmer 202, and allows both positive and negativehalf-cycles of the AC current to flow through the signal detector.Closure of switches R and L also connects the input of the signaldetector 432 to the DH terminal. However, when switch R is closed,current only flows through the signal detector 432 during the positivehalf-cycles of the AC power source 406 because of a diode 434. Insimilar manner, when switch L is closed, current only flows through thesignal detector 432 during the negative half-cycles because of a diode436. The signal detector 432 detects when the switches T, R, and L areclosed, and provides two separate output signals representative of thestate of the switches as inputs to the microcontroller 426. A signal onthe first output of the signal detector 432 indicates a closure ofswitch R and a signal on the second output indicates a closure of switchL. Simultaneous signals on both outputs represents a closure of switchT. The microprocessor controller 426 determines the duration of closurein response to inputs from the signal detector 432.

The remote dimmer 204 provides a means for controlling the dimmer 202from a remote location in a separate wall box. The remote dimmer 204includes a further set of momentary switches T′, R′, and L′ and diodes434′ and 436′. The wire connection is made between the AD terminal ofthe remote dimmer 204 and the AD terminal of the dimmer 202 to allow forthe communication of actuator presses at the remote switch. The ADterminal is connected to the input 440 of the signal detector 432. Theaction of switches T′, R′, and L′ in the remote dimmer 204 correspondsto the action of switches T, R, and L in the dimmer 202.

Since the remote dimmer 204 does not have LEDs, no feedback can beprovided to a user at the remote dimmer 204. Therefore there is a needfor multiple location dimming system in which the remote devices includevisual displays for providing feedback to a user.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a load controlsystem for controlling the power delivered to an electrical load from anAC power source comprises a main load control device and a remote loadcontrol device. The main load control device is operable to control theelectrical load, and to conduct an AC current from the AC power source.The main load control device comprises a load control circuit forcontrolling the amount of power delivered to the electrical load, and areceiver for receiving digital messages, such that the main load controldevice is able to control the electrical load in response to thereceived digital messages. The remote load control device is adapted tobe coupled in series electrical connection with the main load controldevice for conducting the AC current from the AC power source. Theremote load control device comprises a power supply configured to chargefrom the AC power source through the main load control device during afirst time period of a present half-cycle of the AC power source. Thepower supply is configured to charge during time periods in subsequenthalf-cycles that occur at approximately the same time during therespective half-cycle as the first time period occurs during the presenthalf-cycle. The remote load control device further comprises atransmitter for transmitting digital messages. The receiver of the mainload control device and the transmitter of the remote load controldevice are coupled together such that the transmitter of the remote loadcontrol device is able to transmit at least a portion of a digitalmessage to the receiver of the main load control device during a secondtime period of the present half-cycle. The transmitter of the remoteload control device is configured to transmit at least a portion of adigital message to the receiver of the main load control device duringtime periods in subsequent half-cycles that occur at approximately thesame time during the respective half-cycle as the second time periodoccurs during the present half-cycle.

According to another embodiment of the present invention, a load controldevice adapted for use in a load control system having a remote controldevice comprises a load control circuit, a controller, a communicationcircuit, and a switching circuit. The load control circuit is configuredto be coupled to the electrical load for controlling the power deliveredto the electrical load. The controller operatively coupled to the loadcontrol circuit for controlling the power delivered to the electricalload. The switching circuit is configured to be rendered conductive toallow the power supply of the remote control device to charge current inorder to charge during a first time period of a half-cycle of the ACpower source. The controller is configured to render the switchingcircuit conductive to allow the power supply of the remote controldevice to draw current to charge during time periods in subsequenthalf-cycles that occur at approximately the same during the respectivehalf-cycle as the first time period occurs during the presenthalf-cycle. The communication circuit is coupled to the controller forreceiving digital messages. The communication circuit is configured tobe coupled to the transmitter of the remote control device such that thecontroller is configured to receive at least a portion of a digitalmessage from the transmitter of the remote load control device during asecond time period of the half-cycle of the AC power source. Thecontroller is configured to receive at least a portion of a digitalmessage from the transmitter of the remote load control device duringtime periods in subsequent half-cycles that occur at approximately thesame during the respective half-cycle as the second time period occursduring the present half-cycle.

Other features and advantages of the present invention will becomeapparent from the following description of the invention that refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For the purpose of illustrating the invention, there is shown in thedrawings a form, which is presently preferred, it being understood,however, that the invention is not limited to the precise arrangementsand instrumentalities shown. The features and advantages of the presentinvention will become apparent from the following description of theinvention that refers to the accompanying drawings, in which:

FIG. 1A shows a prior art three-way switch system, which includes twothree-way switches;

FIG. 1B shows an example of a prior art three-way dimmer switch systemincluding one prior art three-way dimmer switch and one three-wayswitch;

FIG. 1C shows a prior art four-way switching system;

FIG. 1D shows a prior art extended four-way switching system;

FIG. 2 is a simplified block diagram of a typical prior art multiplelocation lighting control system having a dimmer switch and a remoteswitch;

FIG. 3 is a front view of a user interface of the dimmer switch of themultiple location lighting control system of FIG. 2;

FIG. 4 is a simplified block diagram of the dimmer switch and the remoteswitch of the multiple location lighting control system of FIG. 2;

FIG. 5 is a simplified block diagram of a multiple location dimmingsystem having a main dimmer and two remote dimmers according to a firstembodiment of the present invention;

FIG. 6 is a perspective view of a user interface of the main dimmer andthe remote dimmers of the system of FIG. 5;

FIG. 7 is a simplified block diagram of the main dimmer of the system ofFIG. 5;

FIG. 8 is a simplified schematic diagram of a current limit circuit ofthe main dimmer of FIG. 7;

FIG. 9 is a simplified diagram of a transceiver of the main dimmer ofFIG. 7;

FIG. 10 is a simplified schematic diagram of switching circuits of themain dimmer of FIG. 7;

FIG. 11 is a simplified block diagram of the remote dimmers of thesystem of FIG. 5; and

FIG. 12 is a timing diagram of a complete line cycle of an AC voltagewaveform detailing the operation of the system of FIG. 5.

FIGS. 13A and 13B are simplified flowcharts of a load-sidemulti-location control procedure and a line-side multi-location controlprocedure, respectively, executed by a controller of the main dimmer ofFIG. 7;

FIGS. 14A and 14B are simplified flowcharts of a load-side communicationroutine and a line-side communication routine, respectively, executedduring the load-side and line-side multi-location control procedures ofFIGS. 13A and 13B;

FIGS. 15A and 15B are simplified flowcharts of a load-side RX routineand a line-side RX routine, respectively, executed during the load-sideand line-side communication routines of FIGS. 14A and 14B;

FIGS. 16A and 16B are simplified flowcharts of a load-side TX routineand a line-side TX routine, respectively, executed during the load-sideand line-side communication routines of FIGS. 14A and 14B;

FIG. 17 is a simplified flowchart of a user interface procedure executedby the controller of the main dimmer of FIG. 7;

FIG. 18 is a simplified flowchart of an Idle routine of the userinterface procedure of FIG. 17;

FIG. 19 is a simplified flowchart of an ActiveHold routine of the userinterface procedure of FIG. 17;

FIG. 20 is a simplified flowchart of a Release routine of the userinterface procedure of FIG. 17;

FIG. 21 is a simplified flowchart of a RX buffer procedure executed bythe controller of the main dimmer of FIG. 7;

FIG. 22 is a simplified flowchart of a multi-location control procedureexecuted by controllers of the remote dimmers of FIG. 11;

FIG. 23 is a simplified block diagram of a main dimmer according to asecond embodiment of the present invention;

FIG. 24 is a simplified schematic diagram of the main dimmer of FIG. 23showing first and second gate drive circuits and a current sense circuitin greater detail;

FIG. 25 is a simplified block diagram of a multiple location dimmingsystem having a main dimmer and remote dimmers according to a thirdembodiment of the present invention; and

FIG. 26 is a simplified block diagram of the main dimmer and the remotedimmer of FIG. 25 according to the third embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The foregoing summary, as well as the following detailed description ofthe preferred embodiments, is better understood when read in conjunctionwith the appended drawings. For the purposes of illustrating theinvention, there is shown in the drawings an embodiment that ispresently preferred, in which like numerals represent similar partsthroughout the several views of the drawings, it being understood,however, that the invention is not limited to the specific methods andinstrumentalities disclosed.

FIG. 5 is a simplified block diagram of a multiple location dimmingsystem 500 according to a first embodiment of the present invention. Asshown in FIG. 5, a main dimmer 502 and two remote dimmers 504 (i.e.,accessory dimmers) are coupled in series electrical connection betweenan AC power source 506 and a lighting load 508. The main dimmer 502includes a hot terminal H (i.e., a line-side load terminal) adapted tobe coupled to the line-side of the system 500 and a dimmed-hot terminalDH (i.e., a load-side terminal) adapted to be coupled to the load-sideof the system 500. The main dimmer further comprises a load controlcircuit coupled between the hot and dimmed-hot terminals for controllingthe amount of power delivered to the lighting load 508 (as willdescribed in greater detail with reference to FIG. 7). The remotedimmers 504 include two hot terminals H1, H2, which conduct the loadcurrent from the AC power source 506 to the lighting load 508. The maindimmer 502 and the remote dimmers 504 each comprise accessory dimmerterminals AD coupled together via a single accessory dimmer (AD) line509 (i.e., an accessory wiring). The main dimmer 502 and the remotedimmers 504 are operable to communicate, i.e., transmit and receivedigital messages, via the AD line 509. The main dimmer 502 and theremote dimmers 504 do not require connections to the neutral side of theAC power source 506.

The main dimmer 502 may be wired into any location of the multiplelocation dimming system 500. For example, the main dimmer 502 may bewired in the middle of the two remote dimmers 504, i.e., a first remotedimmer may be wired to the line side of the system 500 and a secondremote dimmer may be wired to the load side of the system 500 (as shownin FIG. 5). Alternatively, the main dimmer 502 may be wired to the lineside or the load side of the system 500. Further, more than two remotedimmers 504 (e.g., up to four remote dimmers) may be provided in themultiple location dimming system 500.

The main dimmer 502 and the remote dimmer 504 all include actuators andvisual displays, such that lighting load 508 may be controlled from andfeedback of the lighting load may be provided at each of the main dimmer502 and the remote dimmers 504. In order to provide the visual displaysat the remote dimmers 504, the remote dimmers each include a controller(e.g., a microprocessor) and a power supply for powering themicroprocessor. The main dimmer 502 provides an AD supply voltage V_(AD)(e.g., approximately 80 V_(DC)) on the AD line 509 to enable the powersupplies of the remote dimmers 504 to charge during a first portion(i.e., a charging time T_(CHRG)) of each half-cycle of the AC powersource 506. During a second portion (i.e., a communication timeT_(COMM)) of each half-cycle, the main dimmer 502 and the remote dimmers504 are operable to transmit and receive the digital messages via the ADline 509.

FIG. 6 is a perspective view of a user interface 600 of the main dimmer502 and the remote dimmers 504. The user interface 600 includes a thintouch sensitive actuator 610 comprising an actuation member 612 havingfirst and second portions 612A, 612B. The actuation member 612 extendsthrough a bezel 614 to contact a touch sensitive device (not shown)located inside the main dimmer 502 (and the remote dimmers 504). Themain dimmer 502 is operable to control the intensity of a connectedlighting load 508 in response to actuations of the actuation member 612of either the main dimmer 502 or the remote dimmers 504.

The user interface 600 further comprises a faceplate 616, which has anon-standard opening 618 and mounts to an adapter 620. The bezel 614 ishoused behind the faceplate 616 and extends through the opening 618. Theadapter 620 connects to a yoke (not shown), which is adapted to mountthe main dimmer 502 and the remote dimmers 504 to standard electricalwallboxes. An air-gap actuator 622 allows for actuation of an internalair-gap switch 722 (FIG. 7) by pulling the air-gap actuator down.

The bezel 614 comprises a break 624, which separates the lower portion612A and the upper portion 612B of the actuation member 612. Uponactuation of the lower portion 612B of the actuation member 612, themain dimmer 502 causes the connected lighting load 508 to toggle from onto off (and vice versa). Actuation of the upper portion 612A of theactuation member 612, i.e., above the break 624, causes the intensity ofthe lighting load 508 to change to a level dependent upon the positionof the actuation along the length of the actuation member 612.

A plurality of visual indicators, e.g., a plurality of light-emittingdiodes (LEDs), are arranged in a linear array behind the actuationmember 612. The actuation member 612 is substantially transparent, suchthat the LEDs are operable to illuminate portions of the actuationmember. Two different color LEDs may be located behind the lower portion612B, such that the lower portion is illuminated, for example, with bluelight when the lighting load 508 is on and with orange light with thelighting load is off. The LEDs behind the upper portion 612A are, forexample, blue and are illuminated as a bar graph to display theintensity of the lighting load 508 when the lighting load is on.

The touch sensitive actuator 610 of the user interface 600 is describedin greater detail in co-pending commonly-assigned U.S. patentapplication Ser. No. 11/471,908, filed Jun. 20, 2006, entitled TOUCHSCREEN ASSEMBLY FOR A LIGHTING CONTROL, and U.S. Provisional PatentApplication Ser. No. 60/925,821, filed Apr. 23, 2007, entitled LOADCONTROL DEVICE HAVING A MODULAR ASSEMBLY. The entire disclosures of bothpatent applications are hereby incorporated by reference.

FIG. 7 is a simplified block diagram of the main dimmer 502 according toa first embodiment of the present invention. The main dimmer 502 employsa bidirectional semiconductor switch 710, e.g., a triac, coupled betweenthe hot terminal H and the dimmed hot terminal DH, to control thecurrent through, and thus the intensity of, the lighting load 508. Thesemiconductor switch 710 could alternatively be implemented as anysuitable bidirectional semiconductor switch, such as, for example, a FETin a full-wave rectifier bridge, two FETs in anti-series connection, orone or more insulated-gate bipolar junction transistors (IGBTs). Thesemiconductor switch 710 has a control input (or gate), which isconnected to a gate drive circuit 712. The input to the gate renders thesemiconductor switch 710 selectively conductive or non-conductive, whichin turn controls the power supplied to the lighting load 508.

A controller 714 is operable to control the semiconductor switch 710 byproviding a control signal to the gate drive circuit 712 using theforward phase control dimming technique. The controller 714 may be anysuitable controller, such as a microcontroller, a microprocessor, aprogrammable logic device (PLD), or an application specific integratedcircuit (ASIC). The controller is coupled to a zero-crossing detectcircuit 716, which determines the zero-crossing points of the AC linevoltage from the AC power supply 506. The controller 714 generates thegate control signals to operate the semiconductor switch 210 to thusprovide voltage from the AC power supply 506 to the lighting load 508 atpredetermined times relative to the zero-crossing points of the AC linevoltage.

The user interface 600 is coupled to the controller 714, such that thecontroller is operable to receive inputs from the touch sensitiveactuator 610 and to control the LEDs to provide feedback of the amountof power presently being delivered to the lighting load 508. Theelectrical circuitry of the user interface 600 is described in greaterdetail in co-pending, commonly-assigned U.S. patent application Ser. No.11/471,914, filed Jun. 20, 2006, entitled FORCE INVARIANT TOUCH SCREEN,the entire disclosure of which is hereby incorporated by reference.

The main dimmer 502 further comprises an audible sound generator 718coupled to the controller 714. The controller 714 is operable to causethe audible sound generator 718 to produce an audible sound in responseto an actuation of the touch sensitive actuator 610. A memory 720 iscoupled to the controller 714 and is operable to store controlinformation of the main dimmer 502.

The air-gap switch 722 is coupled in series between the hot terminal Hand the semiconductor switch 710. The air-gap switch 722 has anormally-closed state in which the semiconductor switch 710 is coupledin series electrical connection between the AC power source 506 and thelighting load 508. When the air-gap switch 722 is actuated (i.e., in anopen state), the air-gap switch provides an actual air-gap break betweenthe AC power source 506 and the lighting load 508. The air-gap switch722 allows a user to service the lighting load 508 without the risk ofelectrical shock. The main dimmer 502 further comprises an inductor 724,i.e., a choke, for providing electromagnetic interference (EMI)filtering.

The main dimmer 502 includes a power supply 730, e.g., a flyback powersupply, which provides both isolated and non-isolated DC outputvoltages. The power supply 730 only draws current at the beginning ofeach half-cycle while the bidirectional semiconductor switch 710 isnon-conductive. The power supply 730 stops drawing current when thebidirectional semiconductor switch 710 is rendered conductive. The powersupply 730 may comprise a transformer (not shown). The power supply 730may provide four output voltages, some of which may be provided byalternate windings of the transformer. The power supply 730 supplies afirst isolated DC output voltage V_(CC1) (e.g., 3.4 V_(DC)) for poweringthe controller 714 and other low voltage circuitry of the main dimmer502. The power supply 730 also generates a second non-isolated DC outputvoltage V_(CC2) (e.g., 80 V_(DC)), for providing power for the AD line509 as will be described in greater detail below. The power supply 730also provides a third non-isolated DC output voltage V_(CC3) (e.g., 12V_(DC)) and a fourth non-isolated DC output voltage V_(CC4) (e.g., 5V_(DC)), which are not shown in FIG. 7. The second, third, and fourthnon-isolated voltages V_(CC2), V_(CC3), V_(CC4) are all referenced to anon-isolated circuit common. An example of the power supply 730 isdescribed in greater detail in commonly-assigned U.S. Provisional PatentApplication Ser. No. 61/015,965, filed the same day as the presentapplication, entitled POWER SUPPLY FOR A LOAD CONTROL DEVICE, the entiredisclosure of which is hereby incorporated by reference.

A current limit circuit 732 is coupled between the second DC outputvoltage V_(CC2) of the power supply 730 and the accessory dimmerterminal AD (via an output connection CLOUT) to provide the AD supplyvoltage V_(AD) to the remote dimmers 504. The current limit circuit 732limits the magnitude of the current provided to the remote dimmers 504to charge the internal power supplies. The controller 714 is operable toadjust the current limit value of the current limit circuit 732 to afirst current limit level (e.g., approximately 150 mA) during thecharging time period T_(CHRG) each half-cycle to limit the current thatthe remote dimmers 504 can draw to charge their internal power supplies.The controller 714 is further operable to adjust the current limit to asecond current limit level (e.g., 10 mA) during the communication timeperiod T_(COMM) each half-cycle. The controller 714 provides a controlsignal I_LIMIT to the current limit circuit 732 to adjust the currentlimit between the first and second current limit levels.

A transceiver 734 allows for the communication of digital messagebetween the main dimmer 502 and the remote dimmer 504. The transceiver734 is coupled to the accessory dimmer terminal AD (via a connectionTX/RX). The transceiver 734 comprises a transmitter 900 (FIG. 9) fortransmitting digital signals on the AD line 509 and a receiver 920 (FIG.9) for receiving digital signals from the remote dimmers 504 coupled tothe AD line. The controller 714 processes the received digital messagesRX_SIG from the receiver 920 and provides the digital messages TX_SIG tobe transmitted to the transmitter 900.

The main dimmer 730 further comprises first and second switchingcircuits 736, 738. The switching circuits 736, 738 are coupled to thedimmed-hot terminal DH and the hot terminal H (through the air-gapswitch 722), respectively. The controller 714 provides a first controlsignal SW1_CTL to the first switching circuit 736 and a second controlsignal SW2_CTL to second switching circuit 738. The controller 714controls the switching circuits 736, 738 to be conductive andnon-conductive on a complementary basis. During the positivehalf-cycles, the controller 714 controls the first switching circuit 736to be conductive, such that the power supply 730, the current limitcircuit 732, and the transceiver 734 are coupled between the accessorydimmer terminal AD and the dimmed-hot terminal DH. This allows theremote dimmer 504 on the load side of the system 500 to charge theinternal power supplies and transmit and receive digital messages duringthe positive half-cycles. During the negative half-cycles, thecontroller 714 controls the second switching circuit 738 to beconductive, such that the power supply 730, the current limit circuit732, and the transceiver 734 are coupled between the accessory dimmerterminal AD and the hot terminal H to allow the remote dimmers 504 onthe line side of the system 500 to charge their power supplies andcommunicate on the AD line 509. Accordingly, the first and secondswitching circuits provide first and second charging paths for theinternal power supplies of the load-side and line-side remote dimmers504, respectively, which both may be enabled by the controller 714.

The main dimmer 502 may also comprise another communication circuit 725(in addition to the transceiver 734) for transmitting or receivingdigital messages via a communications link, for example, a wired serialcontrol link, a power-line carrier (PLC) communication link, or awireless communication link, such as an infrared (IR) or a radiofrequency (RF) communication link. An example of an RF communicationlink is described in commonly assigned U.S. Pat. No. 5,905,442, issuedMay 18, 1999, entitled METHOD AND APPARATUS FOR CONTROLLING ANDDETERMINING THE STATUS OF ELECTRICAL DEVICES FROM REMOTE LOCATIONS, theentire disclosure of which is hereby incorporated by reference.

FIG. 8 is a simplified schematic diagram of the current limit circuit732. The current limit circuit 732 limits the current conducted throughthe accessory dimmer terminal AD. The current through the outputconnection CL_OUT of the current limit circuit 732 is conducted from thesecond non-isolated DC voltage V_(CC2) through a FET Q810 and a diodeD812. The current limit circuit 732 is operable to limit the current totwo discrete current limit levels, i.e., approximately 150 mA and 10 mA,which are controlled in response to the control signal I_LIMIT from thecontroller 714. During normal operation (i.e., when the current throughthe output connection CL_OUT is not exceeding either of the currentlimit levels), the gate of the FET Q810 is coupled to the thirdnon-isolated DC voltage V_(CC3) via two resistors R814, R816 (e.g.,having resistances of approximately 10 kΩ and 470 kΩ, respectively).Accordingly, the voltage at the gate of the FET Q810 is set at theappropriate level such that the FET is conductive. The FET Q840 may bepart number BSP317P, manufactured by Infineon Technologies.

When the control signal I_LIMIT is high (i.e., at approximately themagnitude of the first isolated DC voltage V_(CC1)), the current throughthe output connection CL_OUT of the current limit circuit 732 is limitedto approximately 10 mA. At this time, the current through the outputconnection CL_OUT is conducted from the second non-isolated DC voltageV_(CC2) to the FET Q810 through a first current limit resistor R818(e.g., having a resistance of 220Ω). When the current increases toapproximately 10 mA, the voltage developed across the resistor R818exceeds approximately the base-emitter voltage of a PNP bipolar junctiontransistor (BJT) Q820 plus the forward voltage of a diode D822.Accordingly, the transistor Q820 becomes conductive, thus pulling thegate of the FET Q810 up towards the second non-isolated DC voltageV_(CC2). This causes the FET Q810 to become non-conductive, thuslimiting the current through the output connection CL_OUT toapproximately 10 mA. The transistor Q820 may be part number MBT3906DW,manufactured by On Semicondcutor.

When the control signal I_LIMIT is pulled low to circuit common (i.e.,to substantially zero volts), the current limit is alternatively set at150 mA. Specifically, an NPN bipolar junction transistor Q824 isrendered conductive to couple a second current limit resistor R826 inparallel electrical connection with the first current limit resistor.The second current limit resistor R826 may have a resistance of 3.01 kΩ,such that the resulting equivalent resistance coupled in series betweenthe second non-isolated DC voltage V_(CC2) and the FET Q810 causes thecurrent limit level to increase to approximately 150 mA. The transistorQ824 may be part number MPSA06, manufactured by On Semiconductor.

An input photodiode of an optocoupler U828 is coupled in series with aresistor R830 (e.g., having a resistance of 2.2 kΩ) between the firstisolated DC output voltage V_(CC1) and the control signal I_LIMIT. Anoutput phototransistor of the optocoupler U828 is coupled to the base ofa PNP bipolar junction transistor Q832 (e.g., part number BC856BW,manufactured by Philips Semiconductors) through a resistor R834. Whilethe control signal I_LIMIT is high, the base of the transistor Q832 ispulled down towards the third non-isolated DC voltage V_(CC3) throughthe resistor R834 and a resistor R836, which may have resistances of 4.7kΩ and 220 kΩ, respectively. The optocoupler U828 may be part numberPS2811, manufactured by NEC Electronics Corporation.

When the control signal I_LIMIT is pulled low, the voltage at the baseof the transistor Q832 is pulled up towards the second non-isolated DCvoltage V_(CC2), such that the transistor Q832 becomes non-conductive.Accordingly, the voltage at the base of a PNP bipolar junctiontransistor Q838 is pulled down towards the third non-isolated DC voltageV_(CC3) through two resistors R840, R842, e.g., having resistances of4.7 kΩ and 470 kΩ, respectively. Thus, the transistor Q838 becomesconductive and pulls the base of the transistor Q824 up towards thesecond non-isolated DC voltage V_(CC2), such that the transistor Q824 isconductive and the second current limit resistor R826 is coupled inparallel with the first current limit resistor R818.

FIG. 9 is a simplified schematic diagram of the transceiver 734, whichcomprises the transmitter 900 and the receiver 920. The transmitter 900and the receiver 920 are coupled to the connection RX/TX through twodiodes D910, D930, such that current is only operable to flow from theaccessory dimmer terminal AD into the transmitter 900 and the receiver920. The transmitter 900 comprises an NPN bipolar junction transistorQ912 coupled to the accessory dimmer terminal AD through the diode D910.The transistor Q912 may be part number MMBT6517, manufactured by OnSemiconductor.

The controller 714 is operable to transmit digital messages on the ADline 509 by controlling the transistor Q912 to be conductive andnon-conductive. The digital messages TX_SIG to be transmitted areprovided from the controller 714 to the base of the transistor Q912 viaa resistor R914 (e.g., having a resistance of 10 kΩ). The base of thetransistor Q912 is also coupled to the non-isolated circuit commonthrough a resistor R916 (e.g., having a resistance of 56 kΩ). Theemitter of the transistor Q912 is coupled to the non-isolated circuitcommon through a resistor R918 (e.g., having a resistance of 220Ω). Whenthe digital message TX_SIG provided by the controller 714 is low, thetransistor Q912 remains non-conductive. When the digital message TX_SIGprovided by the controller 714 is high (i.e., at approximately thefourth non-isolated DC voltage V_(CC4)), the transistor Q912 is renderedconductive, thus “shorting” the AD line 509, i.e., reducing themagnitude of the voltage on the AD line to substantially zero volts. Theresistor R918 limits the magnitude of the current that flows through theaccessory dimmer terminal AD when the transistor Q912 is conductive.

The controller 714 is operable to receive digital messages from the ADline 509 via the receiver 920. The receiver 920 comprises a comparatorU932 having an output that provides the received digital messages RX_SIGto the controller 714. For example, the comparator U932 may be partnumber LM2903, manufactured by National Semiconductor. Two resistorsR934, R936 are coupled in series between the DC voltage V_(CC4) andcircuit common and may have resistances of 68.1 kΩ and 110 kΩ,respectively. A reference voltage V_(REF) is generated at the junctionof the resistors R934, R936 and is provided to a non-inverting input ofthe comparator U932. An inverting input of the comparator U932 iscoupled to the accessory dimmer terminal AD through a network ofresistors R938, R940, R942, R944, R946, R948. For example, the resistorsR938, R940, R942, R944, R946, R948 have resistances of 220 kΩ, 68.1 kΩ,220 kΩ, 47.5 kΩ, 20 kΩ, and 220 kΩ, respectively. The output of thecomparator U932 is coupled to the DC voltage V_(CC4) via a resistor R950(e.g., having a resistance of 4.7 kΩ).

The output of the comparator U932 is also coupled to the non-invertinginput via a resistor R952 to provide some hysteresis. For example, theresistor R952 may have a resistance of 820 kΩ, such that when the outputof the comparator U932 is pulled high to the DC voltage V_(CC4), thereference voltage V_(REF) at the non-inverting input of the comparatorU932 has a magnitude of approximately 3.1 V. When the output of thecomparator U932 is driven low, the reference voltage V_(REF) has amagnitude of approximately 2.9 V.

If neither the main dimmer 502 nor the remote dimmers 504 are shortingout the AD line 509, the second non-isolated DC output voltage V_(CC2)(i.e., 80 V_(DC)) is present at the accessory dimmer terminal AD of themain dimmer 502. Accordingly, the inverting input of the comparator U932is pulled up to a voltage of approximately 5 V. Since the voltage at theinverting input of the comparator U932 is greater than the referencevoltage V_(REF) at the non-inverting input, the output of the comparatoris driven low to circuit common (i.e., approximately zero volts). Wheneither the main dimmer 502 or one of the remote dimmer 504 shorts outthe AD line 509, the voltage at the non-inverting input of thecomparator U932 is pulled down below the reference voltage V_(REF),e.g., to approximately 2.2 V, such that the output of the comparator ispulled up to approximately the DC voltage V_(CC4).

FIG. 10 is a simplified schematic diagram of the switching circuit 736,738. The first switching circuit 736 is coupled between the dimmed-hotterminal DH and the non-isolated circuit common. The second switchingcircuit 738 is coupled between the hot terminal H and the non-isolatedcircuit common. During the positive half-cycles, the controller 714controls the first switching circuit 736 to be conductive andnon-conductive via the first control signal SW1_CTL. During the negativehalf-cycles, the controller 714 controls the second switching circuit738 to be conductive and non-conductive via the second control signalSW2_CTL.

The first switching circuit 736 comprises a FET 1010, which conductscurrent from the non-isolated circuit common to the dimmed-hot terminal.For example, the FET 1010 is part number STN1NK60, manufactured by STMicroelectronics, and has a maximum voltage rating of 600 V. The firstcontrol signal SW1_CTL is coupled to the base of an NPN bipolartransistor Q1012 via a resistor R1014 (e.g., having a resistance of 1kΩ). The transistor Q1012 may be part number MBT3904DW, manufactured byOn Semiconductor. When the first control signal SW1_CTL is low (i.e., atapproximately zero volts), the transistor Q1012 is non-conductive, whichallows the gate of the FET Q1010 to be pulled up to approximately thesecond non-isolated DC voltage V_(CC2) via two resistors R1016, R1018,thus rendering the FET 1010 conductive. For example, the resistorsR1014, R1016 may have resistances of 22 kΩ and 470 kΩ, respectively.When the first control signal SW1_CTL is high, the base of thetransistor Q1012 is pulled up to approximately the fourth isolated DCvoltage V_(CC4) via a resistor R1020 (e.g., having a resistance of 100kΩ). Accordingly, the transistor Q1012 is conductive and the gate of theFET 1010 is pulled low towards circuit common, thus rendering the FET1010 non-conductive.

The second switching circuit 738 comprises a FET 1030, which is operableto conduct current from the non-isolated circuit common to the hotterminal. The second switching circuit 738 includes a similar drivingcircuit as the first switching circuit 736 for rendering the FET 1030conductive and non-conductive.

When the FET 1010 of the first switching circuit 736 is conductive, theFET 1030 of the second switching circuit is rendered non-conductive.Specifically, the first switching circuit 736 includes an NPN bipolartransistor Q1022 having a base coupled to the non-isolated circuitcommon through resistor R1024 (e.g., having a resistance of 10 kΩ). Whenthe FET 1010 is conducting current from the non-isolated circuit commonto the dimmed-hot terminal DH, a voltage is produced across a resistorR1026, such that the transistor Q1022 is rendered conductive.Accordingly, the gate of the FET 1030 of the second switching circuit738 is pulled away from the second non-isolated DC voltage V_(CC2) toprevent the FET Q1030 from being conductive while the FET 1010 isconductive. Similarly, the second switching circuit 738 includes an NPNbipolar transistor Q1042, which causes the FET 1010 to be non-conductivewhen the FET 1030 is conducting and the appropriate voltage is producedacross a resistor R1046.

FIG. 11 is a simplified block diagram of one of the remote dimmers 504.The remote dimmer 504 includes many of the same functional blocks as themain dimmer 502. The remote dimmer 504 includes a controller 1114, butdoes not include any load control circuitry (i.e., the bidirectionalsemiconductor switch 710 and the gate drive circuit 712). The remotedimmer 504 comprises first and second hot terminals H1, H2 that arecoupled in series with the bidirectional semiconductor switch 710 of themain dimmer 502, and are adapted to conduct the load current from the ACpower source 506 to the lighting load 508.

A power supply 1130 is coupled between the accessory dimmer terminal ADand the second hot terminal H2 to draw power from the main dimmer 502during the charging time period T_(CHRG) of each half-cycle. The powersupply 1130 only generates one isolated DC output voltage V_(CC1) (e.g.,3.4 V_(DC)) for powering the controller 1114 and other low voltagecircuitry of the remote dimmer 504.

A zero-crossing detector 1116 and a transceiver 1134 are coupled betweenthe accessory dimmer terminal AD and the second hot terminal H2. Thezero-crossing detector 1116 detects a zero-crossing when either of thefirst and second switching circuits 736, 738 change from non-conductiveto conductive, thus coupling the AD supply voltage V_(AD) across thezero-crossing detector. The controller 1114 begins timing at eachzero-crossing and is then operable to transmit and receive digitalmessages via the transceiver 1134 after the charging time periodT_(CHRG) expires. The transceiver 1134 of the remote dimmer 504 iscoupled in parallel with the transceiver 734 of the main dimmer 502forming a communication path during the communication time periodT_(COMM) either in the positive or negative half-cycles depending onwhich side of the system 500 to which the remote dimmer is coupled.Accordingly, the communication path between the main dimmer 502 and theremote dimmers 504 does not pass through the AC power source 506 or thelighting load 508.

If the remote dimmers 504 are wired on both sides of the system 500 suchthat the first hot terminal H1 (which is coupled to the air-gap switch1122) is positioned towards the AC power source 506 or the lighting load508 (as shown in FIG. 5), the opening any of the air-gap switches 1122of the remote dimmers 504 provides a true air-gap disconnect between theAC power source 506 and the lighting load 508. However, opening only theair-gap switch 722 of the main dimmer 502 does not provide a trueair-gap disconnect between the AC power source 506 and the lighting load508. When the air-gap switch 722 is open, the controller 714 does notpower up and does not control either of the switching circuits 736, 738to be conductive. When the air-gap switch 722 is opened and thecontroller 714 is not powered, the magnitude of the leakage currentthrough the accessory dimmer terminal AD is limited (for example, toless than 0.5 mA) such that system 500 still meets the appropriateair-gap standards as set by, for example, the Underwriters Laboratories(UL). Specifically, the zero-crossing detectors 1116, the power supplies1130, and the transceivers 1134 of the remote dimmers 504 include diodescoupled to the accessory dimmer terminal AD, such that the accessorydimmer terminals AD of the remote dimmers are only operable to conductcurrent into the remote dimmers. Thus, the only path for leakage currentthrough the system 500 is through the dimmed hot terminal DH and out ofthe accessory dimmer terminal AD of the main dimmer 502 (i.e., throughthe first switching circuit 736, the power supply 730, and the currentlimit circuit 732). The components chosen for these circuits are suchthat the magnitude of the leakage current through the main dimmer 504 islimited to an appropriate level to meet the UL standard for leakagecurrent when the air-gap switch 722 is opened.

The above-described scenario applies when the main dimmer 502 and theremote dimmers 504 are wired in the system 500 in any fashion. Forexample, the remote dimmers 504 may be wired to the line-side or theload-side of the system 500. Also, the system 500 may include moreremote dimmers 504 than shown in FIG. 5. When any of the main dimmer 502and the remote dimmers 504 are wired directly to the AC power source 506and the lighting load 508, the respective air-gap switches 722, 1122 arepositioned towards the AC power source and the lighting load, such thatopening those air-gap switches provides an true air-gap disconnectbetween the AC power source 506 and the lighting load 508. However, ifany of the main dimmer 502 and the remote dimmers 504 that are wireddirectly to the AC power source 506 and the lighting load 508 do nothave their air-gap switches 722, 1122 positioned towards the AC powersource and the lighting load, the leakage current through the maindimmer and the remote dimmers is limited to meet the UL standard forleakage current when an air-gap switch is opened as described above. Theleakage current is further limited in this way when the air-gap switches722, 1122 of any of the main dimmer 502 and the remote dimmers 504 thatare wired in the middle of the system 500 are opened.

FIG. 12 is a simplified timing diagram of a complete line cycle of an ACvoltage waveform 1200 provided by the AC power source 506. The timingdiagram illustrates the operation of the main dimmer 502 during eachhalf-cycle of the AC voltage waveform 1200. The main dimmer 502 isoperable to allow the remote dimmers 504 to charge their internal powersupplies 1130 during the charging time period T_(CHRG) each half-cycle.The main dimmer 502 and the remote dimmers 504 are operable to transmitand receive digital messages on the AD line 509 during the communicationtime period T_(COMM) each half-cycle. The controller 714 of the maindimmer 502 enables the first switching circuit 736 and the second switchcircuit 738 during a switch time period T_(SW), which is equal to thecharging time period T_(CHRG) plus the communication time periodT_(COMM).

FIG. 13A is a simplified flowchart of a load-side multi-location controlprocedure 1300 executed by the controller 714 of the main dimmer 502 thepositive half-cycles of the AC power source 506. FIG. 13B is asimplified flowchart of a line-side multi-location control procedure1300′ executed by the controller 714 of the main dimmer 502 the negativehalf-cycles of the AC power source 506. The load-side multi-locationcontrol procedure 1300 begins at the beginning of each positivehalf-cycle when the zero-crossing detector 718 of the main dimmer 502signals a positive-going zero-crossing to the controller 714 at step1310. At step 1312, the controller 714 starts a timer, which is used todetermine when the charging time period T_(CHRG) and the communicationtime period T_(COMM) begin and end. The controller 714 then waits atstep 1314 for a wait time period T_(W) (e.g., approximately 10% of apositive half-cycle or 833 μsec).

At step 1316, the controller 714 renders the load-side switching circuit(i.e., the first switching circuit 736) conductive by driving the firstcontrol signal SW1_CTL low at the beginning of the charging time periodT_(CHRG). The controller 714 then controls the current limit circuit 732to have a current limit of 150 mA at step 1318 by driving the controlsignal I_LIMIT low. Accordingly, the second DC output voltage V_(CC2)(i.e., the AD supply voltage V_(AD)) is provided to the remote dimmers504 on the load side of the system 500, and the power supplies 1130 ofthe remote dimmer 504 charge during the charging time period T_(CHRG).The zero-crossing detector 1116 of each of the load-side remote dimmers504 detects a zero-crossing at the beginning of the charging time periodT_(CHRG). For example, the charging time period T_(CHRG) lastsapproximately 2 msec.

After the charging time period T_(CHRG) at step 1320, the controller 714controls the current limit of the current limit circuit 732 toapproximately 10 mA at step 1322 at the beginning of the communicationtime period T_(COMM). The first switching circuit 736 is maintainedconductive during the communication time period T_(COMM), such that theAD line 509 remains at the AD supply voltage V_(AD) (i.e., 80 volts withrespect to the dimmed hot terminal DH) if the main dimmer 502 and theremote dimmers 504 are not presently communicating on the AD line 509.

The main dimmer 502 and the remote dimmers 504 are operable to transmitand receive digital messages during the communication time periodT_(COMM). Specifically, the controller 714 executes a load-sidecommunication routine 1400, which will be described in greater detailwith reference to FIG. 14A. The main dimmer 502 and the remote dimmers504 may encode the transmitted digital messages using Manchesterencoding. However, other encoding techniques that are well known tothose of ordinary skill in the art could be used. With Manchesterencoding, the bits of the digital messages (i.e., either a logic zerovalue or a logic one value) are encoded in the transitions (i.e., theedges) of the signal on the communication link. When no messages arebeing transmitted on the AD line 509, the AD line floats high in an idlestate. To transmit a logic zero value, the transceiver 734 is operableto “short” the AD line 509 to the dimmed hot terminal DH to cause the ADline to change from the idle state (i.e., 80 V_(DC)) to a shorted state(i.e., a “high-to-low” transition). Conversely, to transmit a logic onevalue, the transceiver 734 is operable to cause the AD line totransition from the shorted state to the idle state (i.e., a“low-to-high” transition). The controller 714 renders the FET Q912conductive to short the AD line 509 to the dimmed hot terminal DH whenthe first switching circuit 736 is conductive during the positivehalf-cycles.

For example, the communication time period T_(COMM) may last forapproximately 3.75 msec. Five (5) bits of a transmitted message may betransmitted during the communication time period T_(COMM) of eachhalf-cycle. At the end of the communication time period T_(COMM) at step1324, the first switching circuit 736 is rendered non-conductive at step1326, such that the power supply 730 and the transceiver 734 of the maindimmer 504 are no longer coupled between the accessory dimmer terminalAD and the dimmed hot terminal DH.

During the negative half-cycles, a similar timing cycle occurs.Referring to FIG. 13B, the line-side multi-location control procedure1300′ begins at the beginning of each negative half-cycle when thezero-crossing detector 718 of the main dimmer 502 signals anegative-going zero-crossing to the controller 714 at step 1310′. Thecontroller 714 of the main dimmer 502 renders the line-side switchingcircuit (i.e., the second switching circuit 738) conductive at step1316′, such that the second DC output voltage V_(CC2) is provided to theremote dimmers 504 on the line side of the system 500. Accordingly, theremote dimmers 504 on the line side are operable to charge their powersupplies 1130 from the AD supply voltage V_(AD) during the charging timeperiod T_(CHRG), and to transmit and receive digital messages during thecommunication time period T_(COMM) using a line-side communicationroutine 1400′. The controller 714 renders the FET Q912 conductive toshort the AD line 509 to the hot terminal H when the second switchingcircuit 738 is conductive during the negative half-cycles. At the end ofthe communication time period T_(COMM) at step 1324′, the controller 714renders the second switching circuit 738 conductive at step 1326′.

The digital messages transmitted between the main dimmer 502 and theremote dimmers 504 comprise, for example, four fields: a 3-bitsynchronization (start) symbol, a 5-bit message description, a 7-bitmessage data section, and a 10-bit checksum. The synchronization (start)symbol serves to synchronize the transmission across the series of linecycles required to communicate an entire packet. Typically, the messagedescription comprises a “light level” command or a “delay off” command.The 7-bit message data section of each digital message comprisesspecific data in regards to the message description of the presentmessage. For example, the message data may comprise the actual lightlevel information if the message description is a light level command.Up to 128 different light levels may be communicated between the maindimmer 502 and the remote dimmers 504.

Since only five bits are transmitted each half-cycle, the controller 714uses multiple buffers to hold the digital message to be transmitted andreceived. Specifically, the controller 714 of the main dimmer 502 uses aload-side TX buffer and a line-side TX buffer for digital message totransmit during the positive half-cycles and negative half-cycles,respectively. Further, the controller 714 of the main dimmer 502 alsouses a load-side RX buffer and a line-side RX buffer for digitalmessages received during the positive and negative half-cycles,respectively.

Accordingly, the main dimmers 502 and the remote dimmers 504 areoperable to transmit light level information to each other in responseto actuations of the touch sensitive actuator 150. The main dimmers 502and remote dimmer 504 are then all operable to illuminate the LEDsbehind the actuation member 612 to the same level to indicate theintensity of the lighting load 508.

When the system 500 is wired with the main dimmer 504 in a locationother than the line side or the load side of the system, the digitalmessage transmitted across the AD line 509 cannot pass from load side ofthe system to the line side of the system (and vice versa) due to thebidirectional semiconductor switch 710. Accordingly, if a user touchesthe actuator 610 of a remote dimmer 504 on the load side of the maindimmer 502, a remote dimmer 504 on the line side would not receive themessage. To provide full system capability, the main dimmer 502 has anadditional responsibility of relaying messages from one side of thesystem to the other. In the immediately following half-cycle, the maindimmer 502 broadcasts to the opposite side of the system 500 anycommunication signals that are received in the previous half-cycle.

FIG. 14A is a simplified flowchart of the load-side communicationroutine 1400 executed by the controller 714 of the main dimmer 502during the load-side multi-location control procedure 1300. FIG. 14B isa simplified flowchart of the line-side communication routine 1400′executed by the controller 714 of the main dimmer 502 during theline-side multi-location control procedure 1300′. The controller 714uses two flags RX_LOAD and RX_LINE to keep track of whether thecontroller is presently receiving a digital message during the positiveand negative half-cycles, respectively. The controller 714 also uses twoflags TX_LOAD and TX_LINE to keep track of whether the controller ispresently transmitting a digital message during the positive andnegative half-cycles, respectively.

Referring to FIG. 14A, after calling the load-side communication routine1400, the controller 714 first determines at step 1410 as to whether theflag TX_LOAD is set, i.e., the main dimmer 502 is presently in themiddle of transmitting a digital message to the remote dimmers 504 onthe load side of the system 500. If not, the controller 714 executes aload-side RX routine 1500, which will be described in greater detailbelow with reference to FIG. 15A. If the flag TX_LOAD is set at step1410, but the flag RX_LOAD is set (i.e., the main dimmer 502 ispresently receiving a digital message to the dimmers 504 on the loadside of the system 500) at step 1412, the controller 714 also executesthe load-side RX routine 1500. Otherwise, the controller 714 executes aload-side TX routine 1600, which will be described in greater detailbelow with reference to FIG. 16A.

FIG. 15A is a simplified flowchart of the load-side RX routine 1500. Thecontroller 714 first determines the next bit of the received digitalmessage by sampling the AD line 509 at step 1510. The controller 714samples the AD line 509 periodically, e.g., approximately every 75 μsec.The controller 714 uses a 3^(rd)-order median filter 1512 to filternoise from the bits of the received digital messages. A median filter isdescribed in greater detail in co-pending commonly-assigned U.S. patentapplication Ser. No. 11/644,652, filed Dec. 22, 2006, entitled METHOD OFCOMMUNICATING BETWEEN CONTROL DEVICES OF A LOAD CONTROL SYSTEM, theentire disclosure of which is hereby incorporated by reference. If thecontroller 714 has not collected enough samples at step 1510 to decodethe next bit of the received digital message at step 1514, adetermination is made as to whether the end of the communication timeperiod T_(COMM) has arrived at step 1516. If not, the controller 714samples the AD line 509 again at step 1510 at the next sampling time(i.e., 75 μsec after the last sample). When the controller 714 decodesthe next bit at step 1514 (i.e., determines a low-to-high transition ora high-to-low transition in accordance with Manchester encoding), thecontroller loads the new logical bit (i.e., a logic high or a logic low)into a temporary buffer at step 1518, and then samples the AD line 509again at step 1510 if the end of the communication time period T_(COMM)has not arrived at step 1516.

At the end of the communication time period T_(COMM) at step 1516, thecontroller 714 determines if there are any decoded bits in the temporarybuffer at step 1520. If there are not any decoded bits in the temporarybuffer at step 1520 (i.e., the main dimmer 502 is not presentlyreceiving a digital message from the dimmers 504 on the load side of thesystem 500), the load-side RX routine 1500 simply exits. If there aredecoded bits in the temporary buffer at step 1520, the controller loadsthe decoded bits into the load-side RX buffer at step 1522. Thecontroller 714 also loads the new decoded bits into the front of theline-side TX buffer at step 1524, such that the controller willre-transmit the received bit to the remote dimmers 504 on the line-sideof the system 500 during the next half-cycle.

If the controller 714 has received the beginning of a new message atstep 1526 (i.e., the main dimmer has received the 3-bit synchronizationsymbol of a digital message), the controller 714 sets at step 1528 theflag RX_LOAD (since the main dimmer 502 is presently receiving a digitalmessage in the positive half-cycles) and the flag TX_LINE (since themain dimmer 502 will re-transmit the bits of the digital messagereceived from the remote dimmers 504 on the load-side of the system 500to the remote dimmers on the line-side of the system). If the controller714 has received and loaded an entire message into the load-side RXbuffer at step 1530, the controller clears the flag RX_LOAD at step 1532and the routine 1500 exits.

FIG. 16A is a simplified flowchart of the load-side TX routine 1600. Thecontroller 714 first determines the next bit to transmit on the AD line509 from the load-side TX buffer at step 1610. At step 1612, thecontroller 714 transmits the bit according to Manchester encoding, byeither controlling the AD line 509 through either a low-to-high or ahigh-to-low transition. If the controller 714 has transmitted all of thebits for the entire digital message at step 1614, the controller 714clears the flag TX_LOAD at step 1616 and the routine 1600 exits. If thecontroller 714 has not reached the end of the digital message beingtransmitted at step 1614, and has not reached the end of thecommunication time period T_(COMM) at step 1618, the routine 1600 loopsaround to transmit another bit at steps 1612. At the end of thecommunication time period T_(COMM) at step 1618, the routine 1600 simplyexits.

The line-side communication routine 1400′ of FIG. 14B, which is verysimilar to the load-side communication routine 1400, and is executed bythe controller 714 during communication time period T_(COMM) of thenegative half-cycles, and calls a line-side RX routine 1500′ shown inFIG. 15B and a line-side TX routine 1600′ shown in FIG. 16B. Theline-side RX routine 1500′ and a line-side TX routine 1600′ are similarto the load-side RX routine 1500 and a line-side TX routine 1600,respectively. However, during the line-side RX routine 1500′, thecontroller 714 loads the decoded bit into the line-side RX buffer atstep 1522′ and into the load-side TX buffer at step 1524′. Further,during the line-side TX routine 1600′, the controllers 714 loads thenext bit to transmit from the line-side TX buffer at step 1610′.

FIG. 17 is a simplified flowchart of a user interface procedure 1700executed periodically by the controller 714 of the main dimmer 502,e.g., once every 10 msec. The user interface procedure 1700 selectivelyexecutes one of three routines depending upon the state of the maindimmer 502. If the main dimmer 502 is in an “Idle” state (i.e., the useris not actuating the touch sensitive actuator 610) at step 1710, thecontroller 714 executes an Idle routine 1800. If the main dimmer 502 isin an “ActiveHold” state (i.e., the user is presently actuating thetouch sensitive actuator 610) at step 1720, the controller 714 executesan ActiveHold routine 1900. If the main dimmer 502 is in a “Release”state (i.e., the user has recently ceased actuating the touch sensitiveactuator 610) at step 1730, the controller 714 executes a Releaseroutine 2000.

FIG. 18 is a simplified flowchart of the Idle routine 1800, whichexecuted periodically when the main dimmer 502 is in the Idle state. Thecontroller 714 changes the state of the main dimmer 502 to theActiveHold state when the user actuates the touch sensitive actuator610. Specifically, if there is activity on the touch sensitive actuator610 of the main dimmer 502 at step 1810, an activity counter isincremented at step 1812. Otherwise, the activity counter is cleared atstep 1814. The activity counter is used by the controller 714 to ensurethat the main dimmer 502 changes to the ActiveHold state only inresponse to an actuation of the touch sensitive actuator 610 and not asa result of noise or some other undesired impulse. The use of theactivity counter is similar to a software “debouncing” procedure for amechanical switch, which is well known to one having ordinary skill inthe art. If the activity counter is not less than a maximum activitycounter value A_(MAX) at step 1816, then the state of the main dimmer502 is set to the ActiveHold state at step 1818. Otherwise, the Idleroutine 1800 simply exits.

FIG. 19 is a simplified flowchart of the ActiveHold routine 1900, whichis executed once every half-cycle when the touch sensitive actuator 610is being actuated, i.e., when the main dimmer 502 is in the ActiveHoldstate. First, a determination is made as to whether the user has stoppedusing, i.e., released, the touch sensitive actuator 610. If there is noactivity on the touch sensitive actuator 610 at step 1910, thecontroller 714 increments an “inactivity counter” at step 1912. Thecontroller 714 uses the inactivity counter to make sure that the user isnot still actuating the touch sensitive actuator 610 before entering theRelease mode. If the inactivity counter is less than a maximuminactivity counter value I_(MAX) at step 1914, the ActiveHold routine1900 simply exits. Otherwise, the state of the main dimmer 502 is set tothe Release state at step 1915, and then the routine 1900 exits.

If there is activity on the touch sensitive actuator 610 at step 1910,the controller 714 generates an audible sound at step 1916 using theaudible sound generator 718. Generation of the audible sound isdescribed in greater detail in co-pending commonly-assigned U.S. patentapplication Ser. No. 11/472,245, filed Jun. 20, 2006, entitled TOUCHSCREEN WITH SENSORY FEEDBACK, the entire disclosure of which is herebyincorporated by reference. Next, the controller 714 determines wherealong the length of the actuation member 612 that the touch sensitiveactuator is being actuated at step 1918. If the touch sensitive actuator610 is being actuated in the toggle area, i.e., the lower portion 612Bof the actuation member 612, at step 1920, the controller 714 processesthe actuation of the touch sensitive actuator as a toggle. If thelighting load 508 is presently off at step 1922, the controller 714turns the lighting load on. Specifically, the controller 714 illuminatesthe lower portion 612B of the actuation member 612 blue at step 1924 anddims the lighting load 508 up to the preset level, i.e., the desiredlighting intensity of the lighting load, at step 1926. Further, thecontroller 714 loads a digital message into the load-side and line-sideTX buffers at step 1928. The message description of the digital messagecomprises, for example, a light level command and the message datacomprises the preset level. Finally, the controller 714 sets both theflags TX_LOAD and TX_LINE at step 1930 (since the main dimmer 502 willtransmit the digital message to the remote dimmers 504 on both sides ofthe system 500), and the routine 1900 exits.

If the lighting load is presently on at step 1922, the controller 714illuminates the lower portion 612B of the actuation member 612 orange atstep 1932 and controls the lighting load 508 to off at step 1934. Atstep 1928, the controller 714 loads a digital message into the load-sideand line-side TX buffers, where the message description is a light levelcommand and the message data comprises zero percent (or off). Finally,the controller 714 sets both the flags TX_LOAD and TX_LINE at step 1930,and the routine 1900 exits.

If the touch sensitive actuator 610 is not being actuated in the togglearea at step 1920, the upper portion 612A is being actuated and thelocation of the actuation on the touch sensitive actuator 610 isrepresentative of the desired intensity level of the lighting load 508.At step 1936, the controller 714 illuminates the upper portion 612A ofthe actuation member 612 appropriately, i.e., as a bar graphrepresentative of the present intensity of the lighting load 508. Thecontroller 714 dims the lighting load 508 to the appropriate level asdetermined from the location of the actuation of the touch sensitiveactuator 610 at step 1938. At step 1928, the controller 714 loads theload-side and line-side TX buffers with a digital message having a lightlevel command as the message description and the present intensity levelas the message data. Finally, the controller 714 sets both the flagsTX_LOAD and TX_LINE at step 1930, and the routine 1900 exits.

FIG. 20 is a flowchart of the Release routine 2000, which is executedafter the controller 714 sets the state of the dimmer state to theRelease state at step 1915 of the ActiveHold routine 1900. First, thecontroller 714 stores the present intensity level of the lighting load508 in the memory 718 at step 2010. At step 2012, the controller 714stores four entries of the last digital message to be transmitted inresponse to the actuation of the touch sensitive actuator 610 into theload-side and line-side TX buffers, such that the main dimmer 502 sendsfour additional identical digital messages to the remote dimmers 504 toensure that the remote dimmers received the digital message. Finally,the controller 714 sets the state of the main dimmer 502 to the Idlestate at step 2014, and the Release routine 2000 exits.

The message description of the digital messages transmitted between themain dimmer 502 and the remote dimmers 504 may also comprise an advancedprogramming mode (APM) command, i.e., a command to adjust an advancedprogramming feature, such as a protected preset, or a fade rate. If anadvanced programming mode feature is modified at the main dimmer 502,the main dimmer 502 transmits to the remote dimmers 504 a digitalmessage having the message description containing the APM command andthe message data containing the APM feature to change and the value tochange the APM feature to. For example, the digital message may simplybe transmitted four times during the Release routine 2000. An advancedprogramming mode is described in greater detail in commonly-assignedU.S. Pat. No. 7,190,125, issued Mar. 13, 2007, entitled PROGRAMMABLEWALLBOX DIMMER, the entire disclosure of which is hereby incorporated byreference.

FIG. 21 is a simplified flowchart of a RX buffer procedure 2100 executedperiodically by the controller 714 of the main dimmer 502, e.g., onceevery half-cycle. If there is a digital message in either of theline-side and load-side RX buffers at step 2110, the controller 714determines whether the message description of the digital messagecontains an APM command at step 2112 or a light level command at step2114. If the message description is an APM command at step 2112, the APMfeature is modified in the memory 718 at step 2116 and the procedure2100 exits. If the message description is a light level command at step2116 and the message data of the digital message is zero percent (i.e.,off) at step 2118, the controller 714 illuminates the toggle area (i.e.,the lower portion 612B of the actuation member 612) at step 2120, andcontrols the lighting load 508 to off at step 2122. On the other hand,if the message data for the light level command is an intensity greaterthan zero percent at step 2118, the controller 714 illuminates thetoggle area blue at step 2124, and illuminates the upper portion 612A ofthe actuation member 612 appropriately (i.e., as a bar graphrepresentative of the present intensity of the lighting load 508) atstep 2126. Then, the controller 714 controls the intensity of thelighting load 508 to the appropriate level as determined from themessage data of the digital message at step 2128 and the procedure 2100exits.

FIG. 22 is a simplified flowchart of a multi-location control procedure2200 executed by the controller 1114 of the remote dimmers 504. Theprocedure 2200 begins at step 2210 when the zero-crossing detector 1116signals a zero-crossing to the controller, i.e., at the beginning of thecharging time T_(CHRG) as shown in FIG. 12. First, the controller 1114begins a timer at step 2212. At the end of the charging time T_(CHRG) atstep 2214, the controller 1114 executes a communication routine 2216,which is similar to the load-side communication routine 1400 of FIG. 14Band the line-side communication routine 1400′ of FIG. 14B. However,there is no need for different communication routines and differenttransmitting and receiving buffers for each half-cycles since the remotedimmer 504 only communicate in one of the half-cycles depending uponwhether the remote dimmer is coupled to the line-side or the load-sideof the system 500. At the end of the communication time period T_(COMM)at step 2218, the multi-location control procedure 2200 exits.

Since the digital messages transmitted between the main dimmers 502 andthe remote dimmers 504 may include APM commands, the APM features of theload control system 500 may be modified using the user interface of themain dimmer or any of the remote dimmers. The main dimmer 502 and theremote dimmers 504 may be used to adjust local advanced programmingfeatures (i.e., of the main dimmer 502) and global advanced programmingfeatures (i.e., affecting the main dimmer 502 and all remote dimmers504).

FIG. 23 is a simplified block diagram of a main dimmer 2302 according toa second embodiment of the present invention. The bidirectionalsemiconductor switch of the main dimmer 2302 comprises first and secondFETs 2310, 2311 coupled in anti-series connection for control of theamount of power delivered to the lighting load 508. The FETs 2310, 2311are controlled by a controller 2314 via first and second gate drivecircuits 2312, 2313, respectively. Specifically, the controller 2314 isoperable to control the FETs 2310, 2311 using the reverse phase controldimming technique, such that the FETs are rendered conductive at thebeginning of each half-cycle and then rendered non-conductive a specifictime each half-cycle to control the amount of power delivered to thelighting load 508. The FETs 2310, 2311 may be, for example, part numberFDPF2710T, manufactured by Fairchild Semiconductors. A current senseresistor R2317 is coupled between the FETs 2310, 2311 and generates asense voltage having a magnitude representative of the magnitude of thecurrent flowing through the FETs. The current sense resistor R2317 mayhave, for example, a resistance of 15 mΩ. The junction of the first FET2310 and the current sense resistor R2317 is coupled to the non-isolatedcircuit common.

In addition to controlling the amount of power delivered to the lightingload 508, the FETs 2310, 2311 are also controlled to allow for thecharging of the power supplies 1130 of the remote dimmers 504 and forthe communication of digital messages between the main dimmer 2302 andthe remote dimmers 504. Specifically, the controller 2314 renders bothFETs 2310, 2311 conductive at the beginning of each half-cycle. Duringthe positive half-cycles, the controller 2314 renders the first FET 2310non-conductive at the desired time to control the amount of powerdelivered to the lighting load 508, while appropriately controlling thesecond FET 2311 to couple the current limit circuit 732 and thetransceiver 734 in parallel with the load-side remote dimmers 504 (toallow for the charging of the power supplies 1130 and communication withthe load-side remote dimmers). Similarly, during the negativehalf-cycles, the controller 2314 renders the both FETs 2310, 2311conductive at the beginning of the half-cycles, and then renders thesecond FET 2311 non-conductive to adjust the amount of power deliveredto the lighting load 508, while controlling the first FET 2310 to allowfor the charging of the power supplies 1130 and communication with theline-side remote dimmers 504.

The sense voltage generated across the current sense resistor R2317 isprovided to a current sense circuit 2315, which overrides the control ofthe FETs 2310, 2311 to turn off the FETs in the event of an overcurrentcondition. Specifically, if an overcurrent condition is detected, thecurrent sense circuit 2315 renders the first FET 2310 non-conductiveduring the positive half-cycles and the second FET 2311 non-conductiveduring the negative half-cycles. The FETs 2310, 2311 are maintainednon-conductive for the remainder of the half-cycle, and the controller2310 resets the current sense circuit 2315 before the beginning of thenext half-cycle.

During an overcurrent condition, the controller 2314 is still operableto control the first and second FETs to selectively couple the currentlimit circuit 732 and the transceiver 734 in parallel with the line-sideand load-side remote dimmers 504. When the current sense circuit 2315renders the first FET 2310 non-conductive during the positivehalf-cycles, the controller 2314 controls the second FET 2311 to beconductive to allow for communication with the load-side remote dimmers504. When the current sense circuit 2315 renders the second FET 2311non-conductive during the negative half-cycles, the controller 2134controls the first FET 2310 to be conductive to allow for communicationwith the line-side remote dimmers 504. Therefore, during an overcurrentcondition, the current through the FETs 2310, 2311 is limited whilemaintaining communication between the main dimmer 2302 and the remotedimmers 504.

FIG. 24 is a simplified schematic diagram of the main dimmer 2302showing the first and second gate drive circuits 2312, 2313 and thecurrent sense circuit 2315 in greater detail. The controller 2314provides gate drive control signals GT_DRV1 and GT_DRV2 to the first andsecond gate drive circuits 2312, 2313, respectively. The gate drivecircuits 2312, 2313 are coupled to the FETs 2310, 2311, respectively,via gate resistors 82410, R2411 (e.g., each having a resistance of 47Ω).The first gate drive control signal GT_DRV1 is coupled to the base of anNPN bipolar junction transistor Q2420 of the first gate drive circuit2312 via a resistor R2422, which has, for example, a resistance of 33 kΩWhen the first gate drive signal GT_DRV1 is high (i.e., at approximatelythe fourth non-isolated DC supply voltage V_(CC4)), the gate of thefirst FET 2310 is pulled down towards circuit common through a resistorR2424 (e.g., having a resistance of 1.8 kΩ), thus rendering the firstFET non-conductive. When the first gate drive signal GT_DRV1 is low(i.e., at approximately circuit common), the collector of the transistorQ2420 is pulled up towards the fourth non-isolated DC supply voltageV_(CC4) through a resistor R2426 (e.g., having a resistance of 10 kΩ).Accordingly, the first FET 2310 is rendered conductive. The second gatedrive circuit 2313 has a similar structure and operates in a similarmanner as the first gate drive circuit 2312. The transistors Q2420,Q2430 may be implemented as part of a dual-transistor package, e.g.,part number MMDT3904, manufactured by Diodes, Inc.

The current sense circuit 2315 is responsive to the voltage generatedacross the sense resistor R2317 and thus the current conducted throughthe FETs 2310, 2311. During the positive half-cycles, the first FET 2310controls the amount of power delivered to the lighting load 508. At thistime, the voltage generated across the sense resistor R2317 has anegative magnitude with respect to the non-isolated circuit common. Thecurrent sense circuit 2315 comprises a first comparator U2440 (e.g.,part number LM2903, manufactured by On Semiconductor) for rendering thefirst FET 2310 non-conductive in the event of an overcurrent conditionduring the positive half-cycles. A first reference voltage is providedto the inverting input of the comparator U2440 and is generated by aresistive divider comprising resistors R2442, R2444. For example, theresistors R2442, R2444 may have resistances of 36.5 kΩ and 8.66 kΩ,respectively, such that the first reference voltage has a nominalmagnitude of approximately 1 V. The voltage across the sense resistorR2317 is coupled to the non-inverting input of the comparator U2440 viaa resistor R2446 (e.g., having a resistance of 2.15 kΩ) and thenon-inverting input is pulled up towards the fourth non-isolated DCsupply voltage V_(CC4) via a resistor R2448 (e.g., having a resistanceof 6.8 kΩ).

When an overcurrent condition is not presently occurring, the voltagegenerated across the sense resistor R2317 is such that the magnitude ofthe voltage at the non-inverting input of the comparator U2440 isgreater than the magnitude of the first reference voltage at theinverting input. Therefore, the output of the comparator U2440 is drivenhigh. During an overcurrent condition, the magnitude of the voltagegenerated across the sense resistor R2317 increases, such that themagnitude of the voltage at the non-inverting input of the comparatorU2440 decreases below the magnitude of the first reference voltage, atwhich time, the comparator drives the output low towards circuit common.A capacitor C2450 is coupled to the non-inverting input of thecomparator U2440 to provide some delay in the operation of the currentsense circuit 2315 and has, for example, a capacitance of 150 pF.

The output of the comparator U2440 is coupled to the base of a PNPbipolar junction transistor Q2452 through a resistor R2454 (e.g., havinga resistance of 2.2 kΩ). The base of the transistor Q2452 is pulled uptowards the third non-isolated DC supply voltage V_(CC3) through aresistor R2456 (e.g. having a resistance of 220 kΩ), such that when theoutput of the comparator U2440 is high, the transistor Q2452 is renderednon-conductive. However, during an overcurrent condition when the outputof the comparator U2440 is driven low, the transistor Q2452 is renderedconductive. Accordingly, the voltage at the gate of the first FET 2310is pulled down towards circuit common through a diode D2458 and aresistor R2460 (e.g., having a resistance of 220 kΩ), such that thefirst FET 2310 is rendered non-conductive.

After being rendered conductive, the transistor Q2452 is latched on,such that the first FET 2310 remains non-conductive until the first gatedrive circuit 2312 attempts to control the first FET 2310 to benon-conductive. The first gate drive circuit 2312 is coupled to the baseof an NPN bipolar junction transistor Q2462 through a resistor R2464(e.g., having a resistance of 1 kΩ). When the first gate drive circuit2312 is controlling the first FET 2310 to be conductive and the outputof the comparator U2440 is driven low during an overcurrent condition,the transistor Q2462 is rendered conductive. The voltage at thenon-inverting input of the comparator U2440 is pulled down towardscircuit common through the transistor Q2462 and a diode D2466, such thatthe output of the comparator U2440 remains low and the transistor Q2452remains conductive. When the controller 2314 controls the first gatedrive control signal GT_DRV1 high to turn off the first FET 2310, thebase of the transistor Q2462 is pulled toward circuit common and isrendered non-conductive, thus resetting the current sense circuit 2315.The transistors Q2452, Q2462 may be implemented as part of adual-transistor package, e.g., part number MMDT3946, manufactured byDiodes, Inc.

During the negative half-cycles, the second FET 2311 is operable tocontrol the amount of power delivered to the lighting load 508 and thevoltage generated across the sense resistor R2317 has a negativemagnitude with respect to the non-isolated circuit common. The currentsense circuit 2315 comprises a second comparator U2470 (e.g., partnumber LM2903, manufactured by On Semiconductor) for rendering thesecond FET 2311 non-conductive in the event of an overcurrent conditionduring the negative half-cycles. A second reference voltage is generatedby a resistive divider having two resistors R2472, 82474 and is providedto the non-inverting input of the comparator U2470. The resistors R2472,82474 have resistances of, for example, 22 kΩ and 9.09 kΩ, respectively,such that the second reference voltage has a nominal magnitude ofapproximately 1.5 V. The voltage across the sense resistor R2317 iscoupled to the inverting input of the comparator U2470 via a resistorR2476 (e.g., having a resistance of 3.01 kΩ). The inverting input of thecomparator U2470 is pulled up towards the fourth non-isolated DC supplyvoltage V_(CC4) via a resistor R2478 (e.g., having a resistance of 9.31kΩ).

During normal operation when an overcurrent condition is not occurring,the voltage generated across the sense resistor R2317 is such that themagnitude of the voltage at the inverting input of the comparator U2470is less than the magnitude of the second reference voltage at thenon-inverting input and the output of the comparator U2470 is drivenhigh. The magnitude of the voltage generated across the sense resistorR2317 increases during an overcurrent condition, causing the magnitudeof the voltage at the inverting input of the comparator U2470 toincrease above the magnitude of the second reference voltage. Thus, thecomparator U2470 drives the output low towards circuit common. Acapacitor C2480 is coupled to the non-inverting input of the comparatorU2470 to provide some delay in the operation of the current sensecircuit 2315 and has, for example, a capacitance of 150 pF.

The output of the comparator U2470 is coupled to the base of a PNPbipolar junction transistor Q2482 through a resistor R2484 (e.g., havinga resistance of 2.2 kΩ). When the output of the comparator U2470 ishigh, the base of the transistor Q2482 is pulled up towards the thirdnon-isolated DC supply voltage V_(CC3) through a resistor R2486 (e.g.having a resistance of 220 kΩ), thus rendering the transistor Q2482non-conductive. During an overcurrent condition, the output of thecomparator U2470 is driven low and the transistor Q2482 is renderedconductive. At this time, the voltage at the gate of the second FET 2311is “shorted out” through a diode D2488 and a resistor R2490 (e.g.,having a resistance of 220 kΩ), such that the second FET 2311 isrendered non-conductive.

The second gate drive circuit 2313 is coupled to the base of an NPNbipolar junction transistor Q2492 through a resistor R2494 (e.g., havinga resistance of 1 kΩ). When the second gate drive circuit 2313 iscontrolling the first FET 2311 to be conductive and the output of thecomparator U2470 is driven low during an overcurrent condition, thetransistor Q2492 is rendered conductive. The voltage at thenon-inverting input of the comparator U2470 is pulled down towardscircuit common through the transistor Q2482 and a diode D2488.Accordingly, the output of the comparator U2470 remains low, and thetransistor Q2482 is latched on, such that the second FET 2311 remainsnon-conductive until the second gate drive circuit 2313 renders thesecond FET 2311 non-conductive. The current sense circuit 2315 is resetwhen the controller 2314 controls the second gate drive control signalGT_DRV2 high to turn off the second FET 2311, and the base of thetransistor Q2492 is pulled toward circuit common, rendering thetransistor Q2492 non-conductive. The transistors Q2482, Q2492 may beimplemented as part of a dual-transistor package, e.g., part numberMMDT3946, manufactured by Diodes, Inc.

FIG. 25 is a simplified block diagram of a multiple location dimmingsystem 2500 having a main dimmer 2502 and two remote dimmers 504according to a third embodiment of the present invention. According tothe second embodiment, the main dimmer 2502 must be located on eitherthe load-side of the system 2500 (i.e., directly to the lighting load508 as shown in FIG. 25) or the line-side of the system (i.e., directlyto the AC power source 506).

FIG. 26 is a simplified block diagram of the main dimmer 2500 and theremote dimmer 504 according to the third embodiment of the presentinvention. The main dimmer 2500 comprises a single switching circuit2636 coupled between the dimmed hot terminal DH and the accessory dimmerterminal AD, such that the switching circuit 2636 provides a chargingpath for the power supply 730 of the remote dimmer 504. A controller2614 controls the switching circuit 2636 to be conductive to allow thepower supply 730 of the remote dimmer 504 to charge during a chargingtime each half-cycle of the AC power source 506. After the chargingtime, the switching circuit 2636 is rendered non-conductive. During thecharging time, the power supply 730 is coupled in series between the ACpower source 506 and the lighting load 508. As shown in FIG. 26, theswitching circuit 2636 does not limit the current through the powersupply 730 during the charging time. However, the main dimmer 2502 mayfurther comprises a current limiting circuit (not shown) coupled inseries with the switching circuit 2636 for limiting the current throughthe power supply 730.

The controller 2614 is only operable to render the semiconductor switch710 conductive after the end of the charging time to control the amountof power delivered to the lighting load 508. A transceiver 2634 iscoupled from the hot terminal H to the accessory dimmer terminal AD,such that the transceiver 2634 of the main dimmer 2502 is coupled inparallel with the transceiver 734 of the remote dimmer 504. Thecontroller 2614 is operable to transmit and receive digital messages viathe transceiver 2634 during a communication time immediately followingthe charging time. The main dimmer 2502 further comprising a powersupply 2630, which generates an isolated DC supply voltage V_(CC1) forpowering the controller 2614 and other low-voltage circuitry of the maindimmer.

While the main dimmer 2502 is shown on the load-side of the system 2500in FIGS. 25 and 26, the main dimmer 2502 could alternatively be coupledto the line-side of the system 2500, with the dimmed-hot terminal DHcoupled to the AC power source 506 and the hot terminal H coupled to theremote dimmers 504. Since the main dimmer 2502 is coupled to either theload-side or the line-side of the system 2500, the main dimmer 2502 onlyrenders the switching circuit 2636 conductive and communicates with theremote dimmers 504 during every other half-cycle of the AC power source.For example, when the main dimmer 2502 is coupled to the load-side ofthe system 2500, the main dimmer allows the power supplies 730 of theremote dimmers 504 to charge and communicates with the remote dimmers504 during the positive half-cycles. On the other hand, the main dimmer2502 allows the power supplies 730 of the remote dimmers 504 to chargeand communicates with the remote dimmers 504 during the negativehalf-cycles when the main dimmer is coupled to the line-side of thesystem 2500. The main dimmer 2502 does not need to retransmit digitalmessages in subsequent half-cycles.

Although the present invention has been described in relation toparticular embodiments thereof, many other variations and modificationsand other uses will become apparent to those skilled in the art.Therefore, the present invention should not be limited by the specificdisclosure herein.

The values provided herein for the values and part numbers of thecomponents described herein (e.g., as shown FIGS. 8, 9, 10, 23, and 24)are provided as examples in regards to the embodiments of the presentinvention and should not limit the scope of the present invention. Forexample, it would be well within the capabilities of one having ordinaryskill in the art to modify the values of the components of FIGS. 8, 9,10, 23, and 24 and still obtain the load control system of the presentinvention.

What is claimed is:
 1. A load control system for controlling the powerdelivered to an electrical load from an AC power source, the systemcomprising: a main load control device for controlling the electricalload, the main load control device operable to conduct an AC currentfrom the AC power source, the main load control device comprising a loadcontrol circuit for controlling the amount of power delivered to theelectrical load, the main load control device further comprising areceiver for receiving digital messages, such that the main load controldevice is able to control the electrical load in response to thereceived digital messages; and a remote load control device configuredto be coupled in series electrical connection with the main load controldevice for conducting the AC current from the AC power source, theremote load control device comprising a power supply configured tocharge from the AC power source through the main load control deviceduring a first time period of a present half-cycle of the AC powersource, the power supply configured to charge during time periods insubsequent half-cycles that occur at approximately the same time duringthe respective half-cycle as the first time period occurs during thepresent half-cycle, the remote load control device further comprising atransmitter for transmitting digital messages; wherein the remote loadcontrol device is configured to be coupled in series electricalconnection between the AC power source and the main load control device;and wherein the transmitter of the remote load control device and thereceiver of the main load control device are coupled together such thatthe transmitter of the remote load control device is able to transmit atleast a portion of a digital message to the receiver of the main loadcontrol device during a second time period of the present half-cycle,the transmitter of the remote load control device configured to transmitat least a portion of a digital message to the receiver of the main loadcontrol device during time periods in subsequent half-cycles that occurat approximately the same time during the respective half-cycle as thesecond time period occurs during the present half-cycle.
 2. The loadcontrol system of claim 1, wherein the transmitter of the remote loadcontrol device and the receiver of the main load control device arecoupled together so as to form a communication path during the secondtime period of the present half-cycle.
 3. The load control system ofclaim 2, wherein the main load control device comprises a switchingcircuit that is rendered conductive to form the communication pathbetween the receiver of the main load control device and the transmitterof the remote load control device during the second time period of thepresent half-cycle.
 4. The load control system of claim 2, wherein thecommunication path formed by the main load control device and the remotecontrol device does not pass through the electrical load.
 5. The loadcontrol system of claim 2, wherein the communication path formed by themain load control device and the remote control device does not passthrough the AC power source.
 6. The load control system of claim 1,wherein the remote load control device is configured to be coupled inseries electrical connection with the main load control device betweenthe AC power source and the electrical load.
 7. The load control systemof claim 6, wherein the remote load control device is configured to becoupled to the main load control device through an accessory wiring,such that the transmitter of the remote load control device is able totransmit digital messages to the receiver of the main load device viathe accessory wiring during the second time period.
 8. The load controlsystem of claim 7, wherein the main load control device generates asupply voltage and provides the supply voltage on the accessory wiringto allow the remote load control device to charge the power supply. 9.The load control system of claim 1, wherein the transmitter of theremote load control device is configured to transmit a single digitalmessage to the receiver of the main load control device over multiplehalf-cycles, such that the transmitter transmits a predetermined numberof bits of the single digital message during each of the multiplehalf-cycles.
 10. The load control system of claim 9, wherein the remoteload control device comprises an actuator for receiving a user input,the transmitter configured to transmit the single digital message overthe multiple half-cycles in response to an actuation of the actuator.11. The load control system of claim 1, wherein the main load controldevice and the remote load control device both comprise transceivers,such that the main load control device and the remote load controldevice are able to communicate with each other.
 12. The load controlsystem of claim 1, wherein the second time period occurs after the firsttime period during the present half-cycle.
 13. The load control systemof claim 1, wherein the load control circuit conducts the AC currentthrough the electrical load.
 14. A load control device for controllingthe power delivered to an electrical load from an AC power source, theload control device configured for use in a load control systemincluding a remote control device having a power supply and atransmitter, the load control device comprising: a load control circuitconfigured to be coupled to the electrical load for controlling thepower delivered to the electrical load; a controller operatively coupledto the load control circuit for controlling the power delivered to theelectrical load; a switching circuit configured to be renderedconductive by the controller to allow the power supply of the remotecontrol device to draw current in order to charge during a first timeperiod of a half-cycle of the AC power source, the controller configuredto render the switching circuit conductive to allow the power supply ofthe remote control device to draw current to charge during time periodsin subsequent half-cycles that occur at approximately the same timeduring the respective half-cycle as the first time period occurs duringthe present half-cycle; and a communication circuit coupled to thecontroller for receiving digital messages, the communication circuitconfigured to be coupled to the transmitter of the remote control devicesuch that the controller is configured to receive at least a portion ofa digital message from the transmitter of the remote load control deviceduring a second time period of the half-cycle, the controller configuredto receive at least a portion of a digital message from the transmitterof the remote load control device during time periods in subsequenthalf-cycles that occur at approximately the same time during therespective half-cycle as the second time period occurs during thepresent half-cycle.
 15. The load control device of claim 14, wherein thecommunication circuit is configured to be coupled to the transmitter ofthe remote control device so as to form a communication path during asecond time period of the half-cycle.
 16. The load control device ofclaim 15, wherein the controller is configured to render the switchingcircuit conductive during the second time period to form thecommunication path.
 17. The load control device of claim 14, wherein theload control circuit comprises a bidirectional semiconductor switchhaving a control input, the controller coupled to the control input ofthe bidirectional semiconductor switch for rendering the bidirectionalsemiconductor switch conductive.
 18. The load control device of claim14, further comprising: an accessory terminal configured to be coupledto the remote control device, the switching circuit coupled to theaccessory terminal for allowing the power supply of the remote controldevice to draw current through the accessory terminal, the communicationcircuit coupled to the accessory terminal for receiving digital messagesfrom the transmitter of the remote control device; and a power supplyfor generating a supply voltage, the power supply having an outputoperatively coupled to the accessory terminal, such that the supplyvoltage is provided at the accessory terminal during the first timeperiod.
 19. The load control device of claim 14, wherein thecommunication circuit is configured to receive a single digital messagefrom the transmitter of the remote control device over multiplehalf-cycles, such that the communication circuit receives predeterminednumber of bits of the digital message during each of the multiplehalf-cycles.
 20. The load control device of claim 14, wherein at leastone of the digital messages comprises a command to control the amount ofpower delivered to the load.
 21. The load control device of claim 14,wherein the second time period occurs after the first time period duringthe present half-cycle.
 22. The load control device of claim 14, whereinthe communication circuit comprises a receiver.